fix false positives for unused_parens around unary and binary opera…

…tions

compiler/rustc_lint/src/unused.rs

@@ -569,36 +569,48 @@ trait UnusedDelimLint {
             }
         }
 
-        // Prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`
-        let lhs_needs_parens = {
+        // Check if LHS needs parens to prevent false-positives in cases like `fn x() -> u8 { ({ 0 } + 1) }`.
+        {
             let mut innermost = inner;
             loop {
                 innermost = match &innermost.kind {
-                    ExprKind::Binary(_, lhs, _rhs) => lhs,
+                    ExprKind::Binary(_op, lhs, _rhs) => lhs,
                     ExprKind::Call(fn_, _params) => fn_,
                     ExprKind::Cast(expr, _ty) => expr,
                     ExprKind::Type(expr, _ty) => expr,
                     ExprKind::Index(base, _subscript) => base,
-                    _ => break false,
+                    _ => break,
                 };
                 if !classify::expr_requires_semi_to_be_stmt(innermost) {
-                    break true;
+                    return true;
                 }
             }
-        };
+        }
 
-        lhs_needs_parens
-            || (followed_by_block
-                && match &inner.kind {
-                    ExprKind::Ret(_)
-                    | ExprKind::Break(..)
-                    | ExprKind::Yield(..)
-                    | ExprKind::Yeet(..) => true,
-                    ExprKind::Range(_lhs, Some(rhs), _limits) => {
-                        matches!(rhs.kind, ExprKind::Block(..))
-                    }
-                    _ => parser::contains_exterior_struct_lit(&inner),
-                })
+        // Check if RHS needs parens to prevent false-positives in cases like `if (() == return) {}`.
+        if !followed_by_block {
+            return false;
+        }
+        let mut innermost = inner;
+        loop {
+            innermost = match &innermost.kind {
+                ExprKind::Unary(_op, expr) => expr,
+                ExprKind::Binary(_op, _lhs, rhs) => rhs,
+                ExprKind::AssignOp(_op, _lhs, rhs) => rhs,
+                ExprKind::Assign(_lhs, rhs, _span) => rhs,
+
+                ExprKind::Ret(_)
+                | ExprKind::Break(..)
+                | ExprKind::Yield(..)
+                | ExprKind::Yeet(..) => return true,
+
+                ExprKind::Range(_lhs, Some(rhs), _limits) => {
+                    return matches!(rhs.kind, ExprKind::Block(..));
+                }
+
+                _ => return parser::contains_exterior_struct_lit(&inner),
+            }
+        }
     }
 
     fn emit_unused_delims_expr(

tests/ui/lint/unused/issue-54538-unused-parens-lint.fixed

@@ -32,6 +32,14 @@ fn _no_lint_yeet() -> Result<(), ()> {
     Ok(())
 }
 
+fn _no_lint_ops() {
+    #![allow(unreachable_code, irrefutable_let_patterns)]
+    if ((..{}) == ..{}) {}
+    if (!return) {}
+    loop { match (() = () = () = break {}) {} }
+    while let () = (*&mut false |= true && return) {}
+}
+
 // Don't lint in these cases (#64106).
 fn or_patterns_no_lint() {
     match Box::new(0) {

tests/ui/lint/unused/issue-54538-unused-parens-lint.rs

@@ -32,6 +32,14 @@ fn _no_lint_yeet() -> Result<(), ()> {
     Ok(())
 }
 
+fn _no_lint_ops() {
+    #![allow(unreachable_code, irrefutable_let_patterns)]
+    if ((..{}) == ..{}) {}
+    if (!return) {}
+    loop { match (() = () = () = break {}) {} }
+    while let () = (*&mut false |= true && return) {}
+}
+
 // Don't lint in these cases (#64106).
 fn or_patterns_no_lint() {
     match Box::new(0) {

tests/ui/lint/unused/issue-54538-unused-parens-lint.stderr

@@ -76,7 +76,7 @@ LL +     let _ = |a: u8| 0;
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:56:12
+  --> $DIR/issue-54538-unused-parens-lint.rs:64:12
    |
 LL |     if let (0 | 1) = 0 {}
    |            ^     ^
@@ -88,7 +88,7 @@ LL +     if let 0 | 1 = 0 {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:57:13
+  --> $DIR/issue-54538-unused-parens-lint.rs:65:13
    |
 LL |     if let ((0 | 1),) = (0,) {}
    |             ^     ^
@@ -100,7 +100,7 @@ LL +     if let (0 | 1,) = (0,) {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:58:13
+  --> $DIR/issue-54538-unused-parens-lint.rs:66:13
    |
 LL |     if let [(0 | 1)] = [0] {}
    |             ^     ^
@@ -112,7 +112,7 @@ LL +     if let [0 | 1] = [0] {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:59:16
+  --> $DIR/issue-54538-unused-parens-lint.rs:67:16
    |
 LL |     if let 0 | (1 | 2) = 0 {}
    |                ^     ^
@@ -124,7 +124,7 @@ LL +     if let 0 | 1 | 2 = 0 {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:61:15
+  --> $DIR/issue-54538-unused-parens-lint.rs:69:15
    |
 LL |     if let TS((0 | 1)) = TS(0) {}
    |               ^     ^
@@ -136,7 +136,7 @@ LL +     if let TS(0 | 1) = TS(0) {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:63:20
+  --> $DIR/issue-54538-unused-parens-lint.rs:71:20
    |
 LL |     if let NS { f: (0 | 1) } = (NS { f: 0 }) {}
    |                    ^     ^
@@ -148,7 +148,7 @@ LL +     if let NS { f: 0 | 1 } = (NS { f: 0 }) {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:73:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:81:9
    |
 LL |         (_) => {}
    |         ^ ^
@@ -160,7 +160,7 @@ LL +         _ => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:74:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:82:9
    |
 LL |         (y) => {}
    |         ^ ^
@@ -172,7 +172,7 @@ LL +         y => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:75:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:83:9
    |
 LL |         (ref r) => {}
    |         ^     ^
@@ -184,7 +184,7 @@ LL +         ref r => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:76:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:84:9
    |
 LL |         (e @ 1...2) => {}
    |         ^         ^
@@ -196,7 +196,7 @@ LL +         e @ 1...2 => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:82:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:90:9
    |
 LL |         (e @ &(1...2)) => {}
    |         ^            ^
@@ -208,7 +208,7 @@ LL +         e @ &(1...2) => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:83:10
+  --> $DIR/issue-54538-unused-parens-lint.rs:91:10
    |
 LL |         &(_) => {}
    |          ^ ^
@@ -220,7 +220,7 @@ LL +         &_ => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:94:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:102:9
    |
 LL |         (_) => {}
    |         ^ ^
@@ -232,7 +232,7 @@ LL +         _ => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:95:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:103:9
    |
 LL |         (y) => {}
    |         ^ ^
@@ -244,7 +244,7 @@ LL +         y => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:96:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:104:9
    |
 LL |         (ref r) => {}
    |         ^     ^
@@ -256,7 +256,7 @@ LL +         ref r => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:97:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:105:9
    |
 LL |         (e @ 1..=2) => {}
    |         ^         ^
@@ -268,7 +268,7 @@ LL +         e @ 1..=2 => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:103:9
+  --> $DIR/issue-54538-unused-parens-lint.rs:111:9
    |
 LL |         (e @ &(1..=2)) => {}
    |         ^            ^
@@ -280,7 +280,7 @@ LL +         e @ &(1..=2) => {}
    |
 
 error: unnecessary parentheses around pattern
-  --> $DIR/issue-54538-unused-parens-lint.rs:104:10
+  --> $DIR/issue-54538-unused-parens-lint.rs:112:10
    |
 LL |         &(_) => {}
    |          ^ ^